# Modern Csharp Coding Standards

Write modern, high-performance C# code using records, pattern matching, value objects...

- Repository: https://github.com/Aaronontheweb/dotnet-skills (1244 stars)
- Category: Design
- License: MIT
- Last updated: 2026-10-28
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Aaronontheweb/dotnet-skills --skill modern-csharp-coding-standards -g -a claude-code -y`
Codex: `npx skills add Aaronontheweb/dotnet-skills --skill modern-csharp-coding-standards -g -a codex -y`
Cursor: `npx skills add Aaronontheweb/dotnet-skills --skill modern-csharp-coding-standards -g -a cursor -y`
Gemini CLI: `npx skills add Aaronontheweb/dotnet-skills --skill modern-csharp-coding-standards -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add Aaronontheweb/dotnet-skills`

## Description

Write modern, high-performance C# code using records, pattern matching, value objects, async/await, Span<T>/Memory<T>, and best-practice API design patterns. Emphasizes functional-style programming with C# 12+ features.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Modern C# Coding Standards

## When to Use This Skill

Use this skill when:
- Writing new C# code or refactoring existing code
- Designing public APIs for libraries or services
- Optimizing performance-critical code paths
- Implementing domain models with strong typing
- Building async/await-heavy applications
- Working with binary data, buffers, or high-throughput scenarios

## Reference Files

- [value-objects-and-patterns.md](value-objects-and-patterns.md): Full value object examples and pattern matching code
- [performance-and-api-design.md](performance-and-api-design.md): Span<T>/Memory<T> examples and API design principles
- [composition-and-error-handling.md](composition-and-error-handling.md): Composition over inheritance, Result type, testing patterns
- [anti-patterns-and-reflection.md](anti-patterns-and-reflection.md): Reflection avoidance and common anti-patterns

## Core Principles

1. **Immutability by Default** - Use `record` types and `init`-only properties
2. **Type Safety** - Leverage nullable reference types and value objects
3. **Modern Pattern Matching** - Use `switch` expressions and patterns extensively
4. **Async Everywhere** - Prefer async APIs with proper cancellation support
5. **Zero-Allocation Patterns** - Use `Span<T>` and `Memory<T>` for performance-critical code
6. **API Design** - Accept abstractions, return appropriately specific types
7. **Composition Over Inheritance** - Avoid abstract base classes, prefer composition
8. **Value Objects as Structs** - Use `readonly record struct` for value objects

---

## Language Patterns

### Records for Immutable Data (C# 9+)

Use `record` types for DTOs, messages, events, and domain entities.

```csharp
// Simple immutable DTO
public record CustomerDto(string Id, string Name, string Email);

// Record with validation in constructor
public record EmailAddress
{
    public string Value { get; init; }

The rest: https://github.com/Aaronontheweb/dotnet-skills/blob/HEAD/skills/csharp-coding-standards/SKILL.md